1. Field of the Invention
The present invention relates to a semiconductor device with a low dielectric constant.
2. Description of the Related Art
As semiconductor integrated circuits, multilayer wiring devices and other semiconductor devices have attained greater levels of integration and higher element densities, the wire spacing has become tighter, leading to wiring delays due to the increased capacity between wiring lines.
The wiring delay T is affected by the wiring resistance and capacity between wiring lines, and is a property represented by:T∝CR(with R being wiring resistance and C being capacity between wiring lines).
In this formula, the capacity C between wiring lines is represented by:C=∈S/D with D representing a wire spacing, S, an electrode area (area of facing wire line surfaces), and ∈, a dielectric constant of an insulating material provided between the wiring lines.
Consequently, lowering the dielectric constant of the insulating film is an effective means for reducing wiring delays.
Conventionally, silicon dioxide (SiO2), silicon nitride (SiN), phosphorus silicate glass (PSG) and other inorganic films as well as polyimide and other organic polymers have been used as insulating materials.
However, the relative dielectric constant of CVD-SiO2 films, which are used most commonly in semiconductor devices, is about 4. Even SiOF films, which have been studied as low-dielectric constant CVD films, only have a relative dielectric constant of about 3.3 to 3.5.
Under these circumstances, nanoclustering silica (NCS), which is a silica with uniformly distributed holes with a size on a nanometer order, has been developed as a promising interlayer insulating material with a low dielectric constant. This material has a relative dielectric constant of 2.25, much lower than those of conventional materials, and its use in integrated circuits is being studied.
However, in the case of semiconductor devices using copper wiring lines, the copper used in the wiring is known to diffuse into the insulating film when a silicon oxide substance is used as the interlayer insulating film, detracting from the electrical properties of the insulating layer and critically affecting the operation of the device. Consequently, a film (simply called a diffusion prevention film) aimed at preventing diffusion or like of the copper is disposed between the interlayer insulating film and the wiring lines. See for example, Japanese Patent Application Laid-open No. 2004-146798 (paragraphs 0001 to 0006).